A wireless communication system has been widely used to provide various kinds of communication services such as voice or data services. Generally, a wireless communication system is a multiple access system that can communicate with multiple users by sharing available system resources (bandwidth, transmission (Tx) power, and the like). A variety of multiple access systems can be used, for example, a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system an Orthogonal Frequency Division Multiple Access (OFDMA) system, a Single Carrier Frequency-Division Multiple Access (SC-FDMA) system, a Multi-Carrier Frequency Division Multiple Access (MC-FDMA) system, and the like. In a mobile communication system, a user equipment (UE) may receive information from a base station (BS) via a downlink, and may transmit information to the base station (BS) via an uplink. The information that is transmitted and received to and from the UE includes data and a variety of control information. A variety of physical channels are used according to categories and usages of transmission (Tx) and reception (Rx) information of the UE.
A Multiple Input Multiple Output (MIMO) scheme increases system capacity by simultaneously transmitting multiple data streams (or layers) spatially using two or more transmission/reception (Tx/Rx) antennas in a base station (BS) and a user equipment (UE). The MIMO scheme may include a transmission (Tx) diversity scheme, a spatial multiplexing scheme and a beamforming scheme.
A transmit diversity scheme transmits the same data through multiple transmit (Tx) antennas, such that it can implement reliable data transmission without receiving channel-related feedback information from a receiver. A beamforming scheme is used to increase a signal to interference plus noise ratio (SINR) of a receiver by multiplying weighting values by multiple Tx antennas. In general, since a frequency division duplex (FDD) system has independent uplink (UL) and downlink (DL) channels, high reliability channel information is required to obtain a proper beamforming gain and therefore additional feedback information received from the receiver is used.
On the other hand, a spatial multiplexing scheme for a single user and for multiple users will be described in brief. Spatial multiplexing for a single user is called SM or single user MIMO (SU-MIMO), and assigns several antenna resources of a base station (BS) to one UE. The capacity of a MIMO channel increases in proportion to the number of antennas. Meanwhile, spatial multiplexing for multiple users is called spatial division multiple access (SDMA) or multi-user (MU)-MIMO and distributes several antenna resources or radio space resources of a base station (BS) to a plurality of UEs.
A MIMO scheme includes a single codeword (SCW) method which simultaneously transmits N data streams (or N layers) using one channel encoding block and a multiple codeword (MCW) method which transmits N data streams using M (where M is equal to or less than N (where M≦N)) channel encoding blocks. Each channel encoding block generates independent codewords and each codeword is designed to be able to independently detect errors.